Electric power converting apparatus



Marchl, 1932.. R. B. AYER ELECTRIC POWER CONVERTING APPARATUS Filed Dec.20, 1930 0. G. LOAD CURRENT Inventor: Raymond B. Ager,

MM His Attorneg.

Patented Mar. 1, 1932 STATES PATENT OFLFICE mmense. AYER, orSCHENECTADY, NEW Yonx, ASSIGNOR 'ro GENERAL ELECTRI COMPANY,'ACORPORATION OF NEW YORK ELEc'rnIc' rowan CONVERTING, APPARATUS:

Application flled' necember 20, 1930. Seria1'No.i503,751.

Myinvention relates to electric power con- 1 verting apparatus and moreparticularly to such apparatus including electric valves for convertingalternating current into direct.

' 15 patent apparatus by'means of which any desired' load voltagecharacteristic may be'obtained. My invention constitutes an improvementuponthat covered bythe above patent, i I

It is'an'object of my invention to provide an improved electric powerconverting apparatus utilizing electric valves, by means of whichthevoltage of thedirect current circuit may be controlledoverwide limits.

It is a further object of my invention to provide an improved electricpowerconverting apparatus utilizing electric valves by means of whichany desired load voltage characteristic may be obtained at any pre- 30determined load voltage over a wide rangeof voltage variation.

In accordance with my invention, I utilize a pair of grid controlledelectric valves for transmitting the power from an alternating currentcircuit to a direct current circuit and control the grid potential ofthese valves in accordance with variations in the current in v thedirect current circuit, andwith variations in a predetermined portionofthe voltage of thedirect current circuit.

Fora better understanding of my invention together with other andfurther objects thereof, reference is had to the following descriptiontaken in connection with the accompanyingv drawings and its scope willbe pointed out in the appended claims. Fig. 1 of the accompanyingdrawings diagrammatically illustrates oneembodiment of my invention,while certain operating character- 50 istics thereof are shown in Fig.2.

'sistors 21 and 22 respectively.

Referring more particularly to Fig. 1 of the accompanying drawings, Ihave illustrated an apparatus for receiving alternating current from thecircuit 10, converting it into direct current, and delivering it to thereceiving circuit 11, which is adapted to supply a load device 12. Thisapparatus comprises a transformer 13 and electric valves 14 and 15eachprovided with an anode, a cathode and a'control grid. The primarywinding of the transformer 13 is connected to the supply circuit 10,while the secondary is provided with an electrical midpoint connected tothe negative side of the direct current circuit. The outer terminals ofthis seconda winding are connected to'the anodes of theelectric-valves14 and 15, while the cathodes of these valves areconnected together. and to the positive side of the directcurrentcircuit throughi 0p osite halves of the secondary winding of t efilament transformer 16. The

primary winding of the transformer'lfimay be energized from any suitablealternating current circuit such, for example asthe circuit 10. Thevalves 14 and 15 may be of any of the several types well known in theart, but 'I prefer to use valves of the vapor electric discharge type inwhich the starting of current in the valves is determined by thepotential of the control grid but in which current through the valve maybe interrupted only by reducing its anode potential below its criticalvalue. A potentiometer comprising resistors 17 and 18, either or both ofwhich may be variable, is connected across the direct current circuit11. As shown, theresistor 18 is provided with adjustable connections 19and 20 connected to the control grids of the electric valves 14 and 15through re- The gridsof the valves 14 and 15 may be also connected totheir respective cathodes through resistors 23 and'24 respectively. Ifdesired, a reactor 25 may be connected in series with the direct currentcircuit 11 and a capacitor 26 connected across the circuit in order tosmooth out any ripples in the voltage of this circuit.

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in the art that a detailed explanation is not considered necessary. Ithas been found, however, that by providing the electric valves withcontrol grids as described above, the characteristics of the circuit maybe somewhat changed. Referring now to Fig. 2, curve A represents thevariation of the voltage of the direct current circuit 11 with variationin load current and with the control grids of the electric valvesconnected directly to their respective anodes. lVith this connection,the grid potentials are positive whenever the anode potentials arepositive and each tube is conducting complete half waves of alternatingcurrent. It is seen that this voltage regulation is very poor. With theabove described circuit, however, the voltage regulationmay bematerially improved and the load voltage may be independently controlledat any desired value. It will be noticed that the midpoint of thesecondary winding of the transformer 13 is negative with respect to eachof its outer terminals when the valve associated with the particularouter terminal is conducting. Hence, a small negative bias is maintainedon each of the grids of the valves 1.4 and 15 by means of thepotentiometer 17--18 and the variable connections 19 and 20. \Vheneverelectric valves 14 and 15 conduct current, their contained vapor becomesionized with the result that a certain quantity of positive ions areliberated. hen current flows in these valves and their control grids arecharged negatively, free positive ions are attracted by the grid with aresulting positive ion current flow in the grid circuit. This flow ofpositive ion current in the resistors 21 and 22 and the lower portion ofresistor 18 produces a potential drop in these resistors which isopposed to the negative bias impressed upon the control grid from thepotentiometer 17-18 but is usually smaller in magnitude. The resultingpotential of the control grids of electric valves 14 and 15 is then theresultant of the negative bias derived from potentiometer 1718 and thepositive potential drop in the resistors 21, 22 and 18 and it is thisresultant potential which controls the conductivity of electric valves14 and 15. Thus, for a given setting of the adjustable connections 19and 20, the resultant negative bias on the control grids of the valves14 and 15 will maintain them nonconducting for a small initial portionof their respective half cycles of alternating current, and thus reducethe average voltage of the direct current circuit 11. The setting of theadjustable connections 19 and 20, will, of course, determine themagnitude of this negative bias of the control grids and thus controlthe portions of their respective half cycles, during which the valves 14and 15 are conducting. In this way the voltage of the direct currentcircuit 11 can be controlled at any desired value.

Although the average voltage of the circuit 11 is reduced by theaddition of the above described grid circuit, it has been found that itsvoltage regulation is materially improved. This may be explained by thefact that in case the voltage of the circuit 11 tends to drop below thevalue corresponding to the setting of the adjustable connections 19 and20, the negative bias applied to the grids of the valves 14 and 15 fromthe resistor 18 will correspondingly decrease. As a result of thisdecrease in negative bias, each valve will become conducting at anearlier point in its respective half cycle which will in turn increasenot only the average value of the potential of the circuit 11 directly,but also the positive ion current which will tend to still. furtherneutralize the negative bias derived from the resistor 18 until anequilibrium condition is reached. Obviously a reverse operation willtake place in case of an increase of voltage of the circuit 11. It willbe obvious that the same results may be obtained by varying the value ofresistance of the variable resistor 17. In some cases it may be founddesirable to make the resistors 21 and 22 variable in order to providemore flexible control. The resistors 2-3 and 24 preferably have a veryhigh resistance so that they do not affect the above describedoperation, but serve merely to connect the grids of the valves 14 and 15to their respective cathodes in case the main grid circuits should heaccidentally interrupted.

The voltage regulation curves of the above described circuit are shownby the curves B, C, D, E. and F of Fig. 2 corresponding, respectively.to successively decreasing values of the resistance of the variableresistor 17. It will be obvious that the resistances of the severalresistors 17 to 24 inclusive will be determined by the controlcharacteristics of electric valves 14 and 15 as well as by the voltageof the circuit to which the apparatus is supplying power.

While I have described what I at present consider the preferredembodiment of my invention, it will be obvious to those skilled in theart that various changes and modifications may be made without departingfrom my invention, and I therefore aim in the appended claims to coverall such changes and modifications as fall within the true spirit andscope of my invention.

hat I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. In combination with an electric power converting apparatus includinga direct current circuit, an alternating current circuit and an electricvalve provided with a control grid for transmitting power therebetwcen,means for effecting a predetermined load voltage characteristic of saiddirect current circuit comprising means for impressing upon said controlgrid a predetermined portion of the potential of said direct currentcircuit, and means for impressing upon said control grid a potential ofopposite polarity and variable in accordance with the ionization in saidvalve.

2. In combination, an alternating current circuit, an inductive windingconnected thereto, a direct current circuit one side of which isconnected to the electrical midpoint of said inductive winding, a pairof electric valves provided With control grids and connected between theouter terminals of said inductive winding and the other side of thedirect current circuit, means for 'efiecting a predetermined loadvoltage characteristic of 7 said direct current circuit comprising apotentiometer connected across said direct current circuit andadjustable connections including resistances from said control grids tosaid potentiometer, and a second connection, including a high resistancebetween each control grid and its corresponding cathode.

In witness whereof, I have hereto set my hand this 19th day of December,1930.

' RAYMOND B. AYER.

